ADC typically occurs after years of HIV infection and is associated with low CD4+ T cell levels and high plasma viral loads. It is sometimes seen as the first sign of the onset of AIDS. Prevalence is between 10-20% in Western countries[3] and has only been seen in 1-2% of India based infections.[4][5] With the advent of highly active antiretroviral therapy (HAART), the frequency of ADC has declined in developed countries. HAART may not only prevent or delay the onset of ADC in people with HIV infection, it can also improve mental function in people who already have ADC.

Dementia only exists when neurocognitive impairment in the patient is severe enough to interfere markedly with day-to-day function. That is, the patient is typically unable to work and may not be able to take care of him or herself. Before this, the patient is said to have a mild neurocognitive disorder.

While the progression of dysfunction is variable, it is regarded as a serious complication and, untreated, can progress to a fatal outcome. Diagnosis is made by neurologists who carefully rule out alternative diagnoses. This routinely requires a careful neurological examination, brain scans (MRI or CT scan) and a lumbar puncture to evaluate the cerebrospinal fluid. No single test is available to confirm the diagnosis, but the constellation of history, laboratory findings, and examination can reliably establish the diagnosis when performed by experienced clinicians. The amount of virus in the brain does not correlate well with the degree of dementia, suggesting that secondary mechanisms are also important in the manifestation of ADC.

AIDS Dementia Complex (ADC) is not a true opportunistic infection. It is one of the few conditions caused directly by HIV itself. But it is not quite as simple as that because the central nervous system can be damaged by a number of other causes:

Many researchers believe that HIV damages the vital brain cells, neurons, indirectly. According to one theory, HIV either infects or activates cells that nurture and maintain the brain, known as macrophages and microglia. These cells then produce toxins that can set off a series of reactions that instruct neurons to kill themselves. The infected macrophages and microglia also appear to produce additional factors chemokines and cytokines - that can affect neurons as well as other brain cells known as astrocytes. The affected astrocytes, which normally nurture and protect neurons, also may now end up harming neurons. Researchers hope that new drugs under investigation will interfere with the detrimental cycle and prevent neuron death.

Stage 0.5(Subclinical) Minimal symptoms of cognitive or motor dysfunction characteristic of ADC, or mild signs (snout response, slowed extremity movements), but without impairment of work or capacity to perform activities of daily living (ADL). Gait and strength are normal.

Stage 1(Mild) Evidence of functional intellectual or motor impairment characteristic of ADC, but able to perform all but the more demanding aspects of work or ADL. Can walk without assistance.

Stage 2(Moderate) Cannot work or maintain the more demanding aspects of daily life, but able to perform basic activities of self care. Ambulatory, but may require a single prop.